House Majority Leader Kevin McCarthy said Monday that some Republicans are starting to panic as Donald Trump's primary win in South Carolina increases the probability that the billionaire will emerge as the GOP nominee.

“I think there’s more than a 50 percent chance he’s the nominee,” McCarthy said in an interview on MSNBC's Morning Joe show. “And I think that’s what’s setting in for a lot of people. Could they get their heads around Trump being the nominee?”

The California Republican said the contest for the GOP nomination is now effectively a tw0-person race between Trump and Florida Sen. Marco Rubio.

McCarthy did not say whom he would support for president, but when asked whether Ohio Gov. John Kasich would be effective, he responded, “I think John Kasich would be an excellent president. I think he would be — on paper, he seems like the very best."

He explained that governors in general have better training to become president, saying, “They can’t print more money, they have to balance the budget. They pick a Cabinet, they run agencies they didn’t create and try to make them effective.”

McCarthy predicted that Texas Sen. Ted Cruz would have trouble rebounding from his third-place showing in Saturday's South Carolina primary.

“I thought [Ted] Cruz probably had the best ability of his mapping out, but not winning in South Carolina, that’s very difficult now for him,” McCarthy said. “The bigger advantage is to Trump. He’s got momentum.”

Rubio’s performance in South Carolina, after he stumbled in New Hampshire, was “big,” he added. But when asked to name a state Rubio can win, McCarthy said, “Well, I think that’s very difficult. That’s why advantage goes to Trump.”

The real test will come on March 15, the date of the Republican primary in Rubio’s home state. “It’s winner-take-all. If Rubio can’t win Florida, I think it’s pretty difficult,” McCarthy said.

McCarthy said if Trump becomes the nominee, he can work with him. “I think I can work with anyone that comes out to be the nominee,” he said. “Because I think, fundamentally, whoever wins the nomination wants to be successful.”

Trump has taken the oxygen away from a lot of candidates, McCarthy said. “A lot of people, through no fault of their own -- they ran a conventional campaign when the American public does not want the conventional,” he said.

McCarthy also appeared on CNBC Monday to talk about the House’s agenda. “Whoever becomes the nominee,” he said, “they can grab this agenda from poverty and opportunity to economics to reg reform to tax reform to health care and national security — these are all top issues.”